Electric snap switch



April 5, 1949 A. M. MacFARLAND 2,466,458

ELECTRIC SNAP SWITCH Filed May 16, 1947 IN VEN TOR.

0/4 3022 4%]V0ir/az2ci Patented Apr. 5, 1949 ELECTRIC SNAP SWITCH Allison M. MacFarland, Naperville, 111., assignor to W. T. Neiman, Freeport, Ill.

Original application July 11, 1945, Serial No.

604,382, now Patent No. 2,459,661, dated January 18, 1949. Divided and this application May 16, 1947, Serial No. 748,559

Claims. 1

This invention relates to improvements in electric snap switches. More particularly, the inven tion pertains to snap switches of the type wherein the snap action results from the application of forces applied by a leaf spring system having an unstable dead center position. This application is a division of Allison M. MacFarland copending application Serial No. 604,382, filed July 11, 1945, now Patent No. 2,459,661, dated January 18, 1949.

The object of the invention is to provide a snap switch of improved construction and operating characteristics. The device is extremely simple and adaptable for operation by a wide variety of actuating impulses and over .a broad range of capacities.

In the accompanying drawings,

Fig. 1 is a cross sectional elevation of a complete snap switch embodying the invention;

Fig. 2 is a plan view of the interior of the switch of Fig. 1; and

Fig. 3 is a diagrammatic view of the essential operating elements of the switch.

Briefly, the switch consists essentially of a contact bar anchored at one end and having a free end which moves between stops, one or both of which may be electrical contacts, and leaf spring actuating means. The leaf spring is in the form of a three-tyned fork, the inner tyne forming a tension strip anchored at one end, the outer tynes being compression strips approximately parallel in plan to each other and to the inner tension strip. The three strips are connected together at their ends remote from the tension strip anchorage. The free ends of the compression strips bear against a thrust seat on the contact bar in a direction calculated to place the contact bar in tension from the point of anchorage. The switch is actuated by the application of a force which shifts the position of the butt end of the leaf spring.

The switch mechanism is mounted upon a base 2| of ceramic, thermosetting plastic, or other suitable structural insulating material which, together with cover 2| a, forms a housing for the switch. An electrical contact 22 is fixed upon base 2| and is electrically connected to a suitable switch terminal. A contact bar 23 is anchored or afiixed by means of screw 24 to base 2| and carries a contact 25 at its free end which movable contact is adapted to engage electrical contact 22 to close the switch circuit. Contact bar 23 may be in the form of a thin strip of metal or this member may be formed to increase its resistance to twisting. It is preferably flexible in the direction of movement of the contact bar at least adjacent its anchored end.

Contact bar 23 is actuated and its position con-- trolled by the forces exerted by a leaf spring system. In the particular form of switch illustrated in Figures 1 and 2, this leaf spring 26 is in the form of a three-tyned fork, the three tynes forming separate spring strips. The end of the middle leg or strip 21 is fastened to stationary switch structure. It may be noted that the operation of the switch requires only that this member be anchored to the switch structure, the fixed mounting being illustrated because of the greater convenience in assembly with this arrangement. The ends of the outer tynes or spring strips 28 are stepped in notches or thrust seats 29 provided to receive them by a suitable yoke 29a attached to the contact bar near its free end. These seats face the anchored end of the contact bar and receive the thrust of compression spring Strips 28 outwardly from the anchorage at 24. The length of spring strips 28 and the location of the anchorage of strip '21 are such that strips 28 must be bowed in order to insert their ends in seats 29. The end of tension strip 21 may be convenientlymounted by means of 'an insulating support 30 and rivet or bolt 3|.

In assembling the switch, the outer legs 28 of the leaf spring are depressed, and, being under compressive stress in this position, the butt end of the leaf spring is urged upwardly against the switch actuating plunger 32.

The width of contact bar 23 should be less than the distance between the inner edges of the spring strips 28 to provide clearance for the latter which dip below the level of the contact bar. Any one of several forms of contact bar may be employed.

Operation of the device thus described may be explained by reference to the diagrammatic i1- lustration of the essential operating elements in Fig. 3. In this diagram the character T designates the spring strip which is under tension in the spring system and the character 0 designates a strip which is under compression. The corresponding elements of the switch oi. Figs. 1 and 2 are strips 21 and strips 28, respectively. The character P designates the arrow which represents the downward force applied by means of plunger 32. Other elements of the diagram are readily related to the mechanical counterparts in the switch structure of Figs. 1 and 2 by the similarity of numeral designation.

The switch mechanism diagrammatically illustrated in Fig. 3 is one in which the internal circult isnormally open. The moving contact 25' of contact bar 23' rests upon a stop formed by a portion of insulating base 2 I With the spring system anchored at 3| and the free or butt end of the spring 26' maintained at a given level by the force P, a thrust of force having both horizontal and vertical components is exerted at seat 29' of the contact bar 23'. The portion of the contact bar between seat 29 and the anchorage 24 is under tension, this condition being maintained for all positions of this element.

Analysis of the effective forces of the spring system shows that the vertical component of force applied by the spring to the contact bar at seat 28' may be altered in magnitude and reversed in direction by varying the magnitude of force P and thus the position of the butt end of the spring. As this force is increased, the butt end of leaf spring 26' is depressed, the magnitude of the stresses in tension strip T and compression strip C are increased and the direction of the resultant force applied to the contact bar at seat 29 changes. Although it is theoretically possible to apply a force at P which will result in a horizontal force at step 29 without the vertical components, this being the condition for placing the switch mechanism in dead center position, the system is extremely unstable under such conditions and the dead center status is impossible to attain in practice. Actually, as the force P is increased the downward component-of the force which holds the free or contact end of contact bar 23 against the insulating stop 2| abruptly changes to an upward component which starts the contact 25 in upward motion. This initial displacement of the contact bar moves the point of application of the force of the spring v system at seat 29' upwardly with the result that the upward component of force is increased and the motion of the bar greatly accelerated. The result is a snap action bringing the contact 25' of bar 23' into engagement with contact 22. Similarly, diminution of the force P permits the free end of the leaf spring to move-upwardly, opening of the switch with a snap action.

Special attention is directed to the nature and effect of a lateral as well as a longitudinal force exerted by the compression strip C of the spring system. This leg of the leaf spring, being bowed and depressed below the general level of tension strip T, exerts an upward force upon the contact bar due to the deformation of this spring strip at the point of junction with the butt end of spring 26'. Thus, the compression strip becomes a floating cantilever. This force, which is only one element of the resultant force applied to the thrust seat, has the effect of lowering the dead center position of the contact bar and serves to accentuate the snap action. The latter effect is the result of an increased deformation of compression strip C as the butt end of the spring 26 is depressed, the end of the strip in the thrust seat being below the center of rotation of the opposite end of the strip and thus approached as the butt end of the spring is depressed.

The extent of travel of plunger 32 and the magnitude of the force which must be applied to this plunger in order to operate the switch depends upon the location of this force. In Fig. l the plunger engages the leaf spring near the free end. This force may be applied either at the butt end of the spring or may be applied at any point along the length of the tension strip 21. Downward force-applied, for example, midway .1 n. innntinn n! the inner leg 21 with the outer legs 28 of the spring has the effect of lowering the entire spring assembly at the same time as the free end is depressed. A greater force is required with less displacement and the lowering of the entire spring assembly under the influence of the depressing force appears to improve the snap action.

On the other hand, the switch may be operated with a smaller force and greater plunger travel by extending the free end of the spring in the manner suggested by the diagrammatic illustration of Fig. 3. With this structure, the nexible extension of the leaf spring absorbs a portion of the motion of the plunger and also provides for the absorption of overtravel of the plunger.

It will be appreciated that the form of the several elements of the switch herein described may be altered without departing from the mode of operation of the mechanism. Particularly, avariety of forms of contact bar may be devised with equally successful results, and the leaf spring may have more than three tynes and is.

not necessarily fabricated from a single piece of metal.

Invention is claimed as follows:

1. A snap switch comprising a switch base, a pair of fixed stops at least one of which is an electrical contact mounted in said base, an electrically conductive contact bar anchored at one end to said base and having a free end movable between said stops and thrust seats arranged near said free end and facing the anchored end thereof, spring means for actuating said contact bar, said spring means comprising an integral leaf spring having three spring strips extending in substantial parallelism from a common terminus at the butt end of said leaf spring, the end of the inner spring strip remote from said butt end of said leaf spring being anchored in fixed relation to said base, the outer spring strips being bowed and depressed below the general level of said inner spring strip and having the ends thereof remote from said butt end of said leaf spring stepped in the thrust seats upon said contact bar whereby vertical and longitudinal components of force are applied to said contact bar at said thrust seats, and means responsive to external manipulation for depressing the butt end of said leaf spring to actuate the switch.

2. A snap switch in accordance with claim 1 in which the fixed stops are so arranged that upward movement of the free end of the contact bar is limited to a point at which the thrust seat is below the level of the anchored end of the inner spring strip.

3.'A snap switch comprising a switch base, a pair of fixed stops at least one of which is an electrical contact mounted in said base, an electrically conductive contact bar mounted at one end to said base and having a free end movable between said stops, said contact bar having a flexible portion adjacent the mounted end and a thrust seat on each side near the free end and facing the mounted end thereof, spring means for actuating said contact bar, said spring means comprising an integral leaf spring having three spring strips extending in substantial parallelism from a common terminus at the butt end of said leaf spring, the end of the inner spring strip remote from said butt end of said leaf spring being anchored in fixed relation tosaid base, the outer spring strips being bowed and depressed below the eneral level of said inner spring strip and having the ends thereof remote from said butt end of said leaf spring stepped in the thrust seats upon said contact bar whereby vertical and longitudinal components of force are applied to said contact bar at said thrust seats, and means responsive to external manipulation for depressing the butt end of said leaf spring to actuate the switch.

4. A snap switch comprising a switch base, a pair of fixed stops at least one of which'is an electrical contact mounted in said base, an electrically conductive contact bar mounted at one end to said base and having a free end movable between said stops, said contact bar having a flexible portion adjacent the mounted end and a thrust seat on each side near the free end and facing the mounted end thereof, spring means for actuating said contact bar, said spring means comprising an integral leaf spring having three spring strips extending in substantial parallelism from a common terminus-at the butt end of said leaf spring, the end of the inner spring strip remote from said butt end of said leaf spring being rigidly mounted in fixed relation to said base, i

the outer spring strips being bowed and depressed below the general level of said inner spring strip and having the ends thereof remote from said butt end of said leaf spring stepped in the thrust seats upon said contact bar whereby vertical and longitudinal components of force are applied to said contact bar at said thrust seats, and means responsive to external manipulation for depressing the butt end of said leaf spring to actuate the switch.

5. A snap switch comprising a switch base, a pair of fixed stops at least one of which is an electrical contact mounted in said base, an electrically conductive contact bar anchored at one end to said base and having a free end movable between said stops and thrust seats arranged near said free end and facing the anchored end thereof, spring means for actuating said contact bar, said spring means comprising a leaf spring having three substantially parallelspring strips rigidly joined together at one end thereof, the free end of the inner spring strip being anchored in fixed relation to said base, the outer spring strips being bowed and depressed between the general level of said inner springstrip and having the free ends thereof stepped in the thrust seats upon said contact bar whereby vertical and longitudinal components of force are'applied to said contact bar at said thrust seats, and means responsive to external manipulatiox'i'for depressing the joined ends of said spring strips to activate the switch.

ALLISON M. MACFARLAND- REFERENCES CITED UNITED STATES PATENTS Name Date Eaton Aug. 22, 1939 Number Certificate of Correction Patent No. 2,466,458. April 5, 1949.

ALLISON M. MACFARLAND It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 5, for the Words thrust of read thrust or; line 44, after opening strike out of;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 20th day of September, A. D. 1949.

JOE E. DANIELS,

Assistant Commissioner of Patents. 

